"Urban Respiration" Revealed by Atmospheric O 2 Measurements in an Industrial Metropolis.

Urban regions, which "inhale" O 2 from the air and "exhale" CO 2 and atmospheric pollutants, including harmful gases and fine particles, are the largest sinks of atmospheric O 2 , yet long-term O 2 measurements in urban regions are currently lacking. In this study, we report continuous measurements of atmospheric O 2 in downtown Lanzhou, an industrial metropolis in northwestern China. We found declines in atmospheric O 2 associated with deteriorated air quality and robust anticorrelations between O 2 and gaseous oxides. By combining O 2 and pollutants measurements with a Lagrangian atmospheric transport model, we quantitatively break down "urban respiration" (ΔO 2URB ) into human respiration (ΔO 2RES ) and fossil fuel combustion (ΔO 2FF ). We found increased ΔO 2FF contribution (from 66.92% to 72.50%) and decreased ΔO 2RES contribution (from 33.08 to 27.50%) as O 2 declines and pollutants accumulate. Further attribution of ΔO 2FF reveals intracity transport of atmospheric pollutants from industrial sectors and suggests transportation sectors as the major O 2 sink in downtown Lanzhou. The varying relationships between O 2 and pollutants under different conditions unfold the dynamics of urban respiration and provide insights into the O 2 and energy consumption, pollutant emission, and intracity atmospheric transport processes.